1. Field of the Invention
The present invention relates to a method of manufacturing a stator coil of a rotary electric machine such as an alternator for use in an automotive vehicle.
2. Description of Related Art
A method of manufacturing a stator coil for a rotary electric machine is disclosed, for example, in JP-B2-3118837 and JP-B2-3196738. The stator coil disclosed in these patents has a plurality of U-shaped conductor segments inserted into stator slots in its axial direction. Leg-end portions of the U-shaped conductor segments are electrically connected to one another after the segments are inserted into the stator slots, thereby forming a stator coil. The U-shaped conductor segment has a head portion and a pair of legs extending from the head portion. The pair of legs are inserted into a pair of slots positioned one-pole pitch apart from each other, and legs sticking out of the slots are twisted in a circumferential direction and electrically connected to one another thereby forming the stator coil. Thus, a first coil end is formed by the head portions of the U-shaped conductor segments, and a second coil end is formed by the legs sticking out of a stator core and electrically connected to one another.
The stator coil is manufactured in the following steps. Conductor segments, each having a head portion and a pair of legs extending in parallel from the head portion, are formed from a conductor wire having a rectangular cross-section. The pair of legs extend closely to each other at this stage. The closely positioned pair of legs are separated from each other by twisting them with respect to the head portion, so that one leg is inserted into one slot while the other leg is inserted into another slot-which is positioned one-pole pitch (electric angle π) apart from the one slot. Thus, the U-shaped conductor segments are formed.
Then, the U-shape conductor segments are inserted into respective slots, and the leg portions sticking out of the stator core are bent in a circumferential direction by half a pole-pitch (electric angle π/2). Then, ends of the legs are electrically connected to one another to form a stator coil as a whole.
Four straight conductor portions of the U-shaped segments may be inserted into one slot as shown in the above patents. In this case, a group of small segments and a group of large segments are formed. The pair of conductor portions of the large segment are positioned at an outer most position in the slot and at an inner most position, while the pair of conductor portions of the small segment are positioned at an inside space between the outer most and the inner most positions.
In some alternators, three compound-phase coils are used to form a three-phase stator coil. For example, it is known to form the three compound-phase coils using six phase coils, U, V, W, X, Y and Z. In this case, U and X phase coils are connected in series forming a U-X compound-phase coil. Similarly, a V-Y compound-phase coil is formed by connecting V and Y phase coils in series, and a W-Z compound-phase coil is formed by connecting W and Z phase coils in series. One pole-pitch (electric angle n) is constituted by six slots, and the six slots are arranged in an order of U, X, -V, Z, W, Y, -U, -X, V, Z, -W and -Y.
A slot pitch between a pair of legs of a U-shaped conductor segment forming an inter-phase connector (e.g., between U and X phases) has to be made different from a slot pitch of other regular U-shaped conductor segments. The same is applied to a U-shaped conductor segment forming an output terminal (e.g., a U-X phase output terminal) and a neutral point connector (e.g., a connector connecting the X-phase to a neutral point of the three-phase winding). For example, if the slot pitch of the regular segment is 6 slots, the slot pitch of the former is 7 slots, and that of the latter is 5 slots. That is, it is required to form regular segments having a regular slot pitch and special segments having a different slot pitch. In other words, an amount of twist given to the head portions of the U-shaped conductor segments has to be changed according to types of the segments. Accordingly, the process for manufacturing the stator coil has not been simple.